Automatic tuning system for radio receivers



3E 23, 1936. K. M. MCLAUGHLIN 2,045,091

AUTOMATIC TUNING SYSTEM FOR RADIO RECEIVERS Filed Aug. 14, 1954AUTOMATIC KNNE7H MERE/LL NCLAUGHL/N PER ATTORNEY Patented June 23, 1936UNITED STATES PATENT OFFICE AUTOMATIC TUNING SYSTEM FOR RADIO RECEIVERSsylvania Application August 14, 1934, Serial No. 739,717

3 Claims.

My invention relates to automatic tuning systems for radio receivers. Inautomatic tuning systems one of the problems is the elimination of audiosignals from undesired stations as the automatic mechanism tunes throughthe undesired signals to the desired signal. I am aware that severalsolutions have been offered; such as, short circuiting the audioresponsive element by means of relays, or governors operating open orclosed circuiting switches.

One of the objects of my invention is a simplified and improved systemof eliminating undesired audio responses as the automatic tuning meanstunes to desired signals. Another object is a system which permits theaudio responsive element to gradually respond to the desired signalinstead of abruptly operating at full intensity. A further object is toproportion the electrical constants of the means for eliminating theundesired stations with respect to the means for automatic tuning sothat the operation of the one depends upon the other.

The single figure of the drawing shows the apparatus and circuitemployed.

The details of my device may be best understood by referring to theaccompanying draw-. ing. I represents a conventional commercial supplyof alternating current, for example 110 volts, 60 cycles. 2 is astep-down transformer which may have a secondary voltage of abouttwenty-four volts. The secondary 3 of transformer 2 is grounded at 4,and connected to the automatic tuning motor 5 by conductor 6. The motor5 in turn connects to motor tripping solenoid 1. The other terminal ofthe solenoid connects to switch arm 8 of triple pole triple positionswitch 9, and also to one terminal of the high impedance winding ofrelay I and switch arm I I. The remaining terminal of the winding ofrelay I0 connects to the off terminal I2, the manual terminal I3 ofswitch 9, and to the off terminals H on time clock face I 5.

Contact arm IB of time clock I is advanced every minutes to one of thecontact studs II. The contact arm I6 is connected by wire I8 to terminalI9 of switch 9. The clock face I5 also contains a series of flexibleleads and plugs. The pairs of leads A to G each correspond to particularstations which may be selected by the user. The ends of these leadsinclude plugs which may be plugged into terminals ll at the desiredhours of operation or connection H may be used to turn off the radioreceiver at a predetermined time. Each of the terminals A to H areelectrically connected to a corresponding brush A to H which in turncontacts commutators A" to H on shaft 22 which is grounded at 23. Theshaft 23 is mechanically connected to the tuning mechanism of the radioreceiving set which is not shown. The radio set may be any receiver ofthe broadcast types now commercially available. Each of the commutatorsA to H" has an insulated segment such as 24. Each commutator may beadjusted on shaft 22 so that the circuit from the commutator through itscorresponding brush will be interrupted by the insulated segment whenthe tuning mechanism of the radio receiver is set at the desiredincoming signal.

The clock mechanism, the commutator arrangement, the motor drive andtripping solenoid are not part of my invention but are fully describedin the co-pending application Serial No. 719,266, filed April 6th, 1934by Mandel and Schoebel.

The transformer 25 for supplying power to the radio receiving set isconnected in parallel to the power source I and consists of transformer25 whose primary 26 is connected to the power source through thecontacts 21 and 28 of relay Ill.

The operation of the invention is as follows: The flexible lead G isconnected to the clock terminal corresponding to 4:30. Contact blade I6has made connection with the 4:30 terminal 30 Contacts 27 and 28 areopen and The circuit from 23 continues through 22, com- 4 mutator G",brush G, and back to G.

The current flowing through this circuit starts motor 5 and the motortrip solenoid I. The motor trip solenoid mechanically couples the driveshaft of the motor to the shaft 22 as described in the above mentionedpending application of Mandel and Schoebel. The shaft is rotated untilthe insulated section 24 of G engages G', and thus interrupts the motorand solenoid circuits by including in their path the high impedancewinding of relay I0 whose circuit is now completed through brush H andcommutator H" to ground 23.

The impedance of the relay winding is chosen so high relative to themotor tripping solenoid and the motor circuit that the current flow willoperate the relay but will be totally insuificient to operate the motoror solenoid. By the way of example, I have found a solenoid impedance of1.25 ohms, a motor impedance of 7.0 ohms, and a relay of 465 ohmsimpedance (all measured at 60 cycles) satisfactory. The current throughI0 is sufiicient to attract 2i and make contact through 28. 27, 23 tothe power supply energizes the radio receiver and permits the signals togradually build up in the audio responsive element of the receiver.

It should be observed that H" is the commutator for an automatic offposition which may be selected by connecting the terminal plug of H intothe desired clock contact stud. The commutator H" is so adjusted that Hmakes contact with H at all positions corresponding to tuning positionsof the other commutators A" to G". The insulated section 24 of H"engages H outside of the usual tuning range of the radio receiver. Whenthe switch 9 is placed in the off position, I!) is short circuited andthe tuning mechanism automatically operated until I-I rests on theinsulated section of H.

During the operation with switch 9 on the off position no signals willbe heard because 21 will not contact 28. With switch 9 on the manualposition, relay I!) will be energized which permits manual operation ofthe receiver but the motor and motor tripping solenoid circuits areshort circuited thereby preventing automatic operation.

The switch 29 is a reversal switch which is used to reverse thedirection of rotation of the commutators and tuning mechanism asdescribed in the above mentioned Mandel and Schoebel application.

It should be understood that a manual switch box may take the place ofclock mechanism IE or may be used concurrently.

In the alternating current operated broadcast receivers, thermionictubes are employed. About thirty seconds is required to heat thecathodes of these tubes to the proper operating value. During the laterpart of this interval the tubes gradually come up in operatingefliciency, and permit a gradual response to incoming signals.

If the tubes are turned oii for about ten seconds, then turned on, theywill begin to operate within one or two seconds. The operating efli- Thecompletion of the circuit of 26 through ciency gradually increases andafter ten seconds the efficiency is about a maximum. I employ this timelag and gradual restoration of operating efficiency. As I have describedabove the power supply to the radio receiver is disconnected duringautomatic tuning. The maximum automatic tuning time has been adjusted toten seconds. After initial operation the radio receiver responds withinone or two seconds to the desired signals, the audio response increasingto full value with the increasing operating efficiency of the tubes. Theefiect on the listener is a pleasant and gradual fading in of thedesired signal.

I claim:

1. The combination of a radio tuning system, an electric motor ofrelatively low impedance for automatically tuning said radio system, asource of power for said motor and said system, a relay having arelatively high impedance winding for de-energizing said radio systemduring the operation of said motor, and circuit connections for seriallyconnecting said low impedance motor and said high impedance relay afterautomatically tuning to a desired signal.

2. The combination of a radio tuning system, an electric motor ofrelatively low impedance for automatically tuning said radio system, asource of power for said motor and said system, a relay having arelatively high impedance winding for disconnecting said power from theradio system during the operation of said motor, and connections forserially connecting said motor and said relay upon termination ofoperation of said motor, whereby said high impedance relay preventsoperation of said low impedance motor.

3. The combination of a radio tuning system, an electric motor ofrelatively low impedance for automatically tuning said radio system, asource of power for said motor and said system, a relay having arelatively high impedance winding for disconnecting said power from theradio system during the operation of said motor and connecting saidpower to the radio system upon completion of automatic tuning of adesired signal by said motor, and connections for serially connectingsaid motor and said relay upon termination of operation of said motor,whereby said high impedance relay prevents operation of said lowimpedance motor.

KENNETH MERRILL McLAUGHLIN.

